Method and system for a light source assembly supporting direct coupling to an integrated circuit

ABSTRACT

Methods and systems for a photonically enabled complementary metal-oxide semiconductor (CMOS) chip are disclosed. The CMOS chip may comprise a laser, a microlens, a turning mirror, and an optical bench, and may generate an optical signal utilizing the laser, focus the optical signal utilizing the microlens, and reflect the optical signal at an angle defined by the turning mirror. The reflected optical signal may be transmitted into the photonically enabled CMOS chip, which may comprise a non-reciprocal polarization rotator, comprising a latching faraday rotator. The CMOS chip may comprise a reciprocal polarization rotator, which may comprise a half-wave plate comprising birefringent materials operably coupled to the optical bench. The turning mirror may be integrated in the optical bench and may reflect the optical signal to transmit through a lid operably coupled to the optical bench.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of application Ser. No. 13/455,641filed on Apr. 25, 2012, which is a continuation of application Ser. No.12/500,465 filed on Jul. 9, 2009, which in turn makes reference to,claims priority to and claims the benefit of U.S. Provisional PatentApplication No. 61/079,358 filed on Jul. 9, 2008.

This application also makes reference to:

U.S. Patent Application Ser. No. 61/190,857 filed on Sep. 3, 2008.

Each of the above stated applications is hereby incorporated herein byreference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

FIELD OF THE INVENTION

Certain embodiments of the invention relate to optoelectroniccommunications. More specifically, certain embodiments of the inventionrelate to a method and system for a light source assembly supportingdirect coupling to an integrated circuit.

BACKGROUND OF THE INVENTION

Optical communication has revolutionized how information is transmitted.Mass-produced semiconductor lasers transmit multiple-wavelength opticalsignals over low-loss, low-dispersion optical fibers, modulated atmulti-gigabit per second (GB/s) rates, for hundreds of kilometers. Text,voice, audio, and video data are all transmitted around the globeutilizing optical fibers, supporting both wired and wirelesscommunication systems.

Optical fiber communication has moved into lower cost, yet still highperformance applications, such as metro access networks and enterpriseLAN backbones. Single-mode fiber (SMF) is poised to replace short copperlinks in high data rate, 10 GB/s and above, applications.

As data networks scale to meet ever-increasing bandwidth requirements,the shortcomings of copper data channels are becoming apparent. Signalattenuation and crosstalk due to radiated electromagnetic energy are themain impediments encountered by designers of such systems. They can bemitigated to some extent with equalization, coding, and shielding, butthese techniques require considerable power, complexity, and cable bulkpenalties while offering only modest improvements in reach and verylimited scalability. Free of such channel limitations, opticalcommunication has been recognized as the successor to copper links.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present invention as set forth inthe remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for a light source assembly supporting directcoupling to an integrated circuit, substantially as shown in and/ordescribed in connection with at least one of the figures, as set forthmore completely in the claims.

Various advantages, aspects and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a block diagram of an exemplary CMOS wafer comprisingoptoelectronic transceiver chips, in accordance with an embodiment ofthe invention.

FIG. 1B is a block diagram of an exemplary integrated CMOS transceiver,in accordance with an embodiment of the invention.

FIG. 1C is a block diagram of an exemplary photonically enabled CMOSchip with guard ring, in accordance with an embodiment of the invention.

FIG. 1D is a block diagram of an exemplary photonically enabled CMOSchip with guard ring, light source, and optical fiber cable, inaccordance with an embodiment of the invention.

FIG. 2A is a block diagram of an exemplary micropackaged light source,in accordance with an embodiment of the invention.

FIG. 2B is a light source assembly functional block diagram, a couplinggeometry diagram, and a micrograph of a functioning grating coupler, inaccordance with an embodiment of the invention.

FIG. 2C is a block diagram of an exemplary photonically enabled CMOSchip, in accordance with an embodiment of the invention.

FIG. 2D is a block diagram of an exemplary optical input/output, inaccordance with an embodiment of the invention.

FIG. 3A is a schematic of a light source assembly comprising a laser, aball lens, an isolator, and a turning mirror incorporated in ahermetically sealed package, in accordance with an embodiment of theinvention.

FIG. 3B is a block diagram of a support substrate with exemplarydimensions, in accordance with an embodiment of the invention.

FIG. 3C is a block diagram of a lid for hermetic sealing of the lightsource assembly, in accordance with an embodiment of the invention.

FIG. 3D is a block diagram of a turning mirror, in accordance with anembodiment of the invention.

FIG. 3E is a block diagram illustrating an exemplary bond padconfiguration, in accordance with an embodiment of the invention.

FIG. 3F is a diagram of an exemplary light source assembly, inaccordance with an embodiment of the invention.

FIG. 3G is a diagram illustrating various views of the light sourceassembly, in accordance with an embodiment of the invention.

FIG. 3H illustrates an exemplary light source module, in accordance withan embodiment of the invention.

FIG. 3I illustrates an exemplary light source module with landing pads,in accordance with an embodiment of the invention.

FIG. 3J illustrates an alternative embodiment of the light sourceassembly where the faraday rotator is encased within pyrex and quartz orsapphire layers below the silicon substrate.

FIG. 3K is a diagram illustrating various views of the light sourceassembly, in accordance with an embodiment of the invention.

FIG. 4A is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.

FIG. 4B is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.

FIG. 4C is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.

FIG. 4D is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.

FIG. 4E is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.

FIG. 5 illustrates a TO-can implementation, in accordance with anembodiment of the invention.

FIG. 6A illustrates a light source assembly with a TO-can and aedge-emitting laser diode implementation with an external heatsink, inaccordance with an embodiment of the invention.

FIG. 6B illustrates a light source assembly implementation having acavity-down wire bond edge-emitting laser diode with an externalheatsink, in accordance with an embodiment of the invention.

FIG. 7 illustrates an alternative embodiment with a cavity-up wire bondimplementation, in accordance with an embodiment of the invention.

FIG. 8 illustrates a cavity-up wire bond implementation with heatspreader, in accordance with an embodiment of the invention.

FIG. 9 is an external heatsink flip-chip implementation of a lightsource assembly, in accordance with an embodiment of the invention.

FIG. 10 illustrates an exemplary module assembly comprising a TO-canoptical source implementation, in accordance with an embodiment of theinvention.

FIG. 11 illustrates exemplary flex circuit bend radius limitationswithin a module, in accordance with an embodiment of the invention.

FIG. 12 illustrates an alternative implementation comprising a laserdiode on a submount coupled to a leadless chip carrier (LCC) package, inaccordance with an embodiment of the invention.

FIG. 13 illustrates an LCC package module implementation, in accordancewith an embodiment of the invention.

FIG. 14 illustrates the non-normal incidence of the optical mode fromthe LCC package, in accordance with an embodiment of the invention.

FIG. 15 illustrates an LCC package with a laser diode on submountimplementation, in accordance with an embodiment of the invention.

FIG. 16 illustrates a cavity-down implementation utilizing thermalgrease, in accordance with an embodiment of the invention.

FIG. 17 is a simplified illustration of an exemplary light sourceassembly, in accordance with an embodiment of the invention.

FIG. 18 illustrates an exemplary light source assembly enclosed in ahermetic package by a lid over the substrate, in accordance with anembodiment of the invention.

FIG. 19 illustrates an LCC package with a hermetically sealed windowlid, in accordance with an embodiment of the invention.

FIG. 20 illustrates the integration of the hermetically sealed LCCpackage onto the CMOS chip and associated printed circuit board andinterconnects, in accordance with an embodiment of the invention.

FIG. 21 illustrates an alternative embodiment utilizing a ring todetermine vertical distance between the laser diode source assembly andthe CMOS die, in accordance with an embodiment of the invention.

FIG. 22 illustrates the desired polarization for increased gratingcoupling efficiency into a single polarization grating coupler in theCMOS chip, in accordance with an embodiment of the invention.

FIG. 23. illustrates a TO can implementation polarization configuration,in accordance with an embodiment of the invention.

FIG. 24 illustrates the challenge of supplying the appropriatepolarization when using a flat-stacked laser diode chip on a mesa, inaccordance with an embodiment of the invention.

FIG. 25 illustrates a laser diode source assembly with a faraday rotatorplus a half-wave plate, in accordance with an embodiment of theinvention.

FIG. 26 illustrates the optical mode polarization without an isolator,in accordance with an embodiment of the invention.

FIG. 27 illustrates several embodiments of external integration forcoupling light into a CMOS photonics chip, in accordance with anembodiment of the invention.

FIG. 28 illustrates an exemplary co-packaging embodiment, in accordancewith an embodiment of the invention.

FIG. 29 illustrates an exemplary co-packaging embodiment with a laserdiode mounted on a heat sink and angled holder, in accordance with anembodiment of the invention.

FIG. 30 illustrates exemplary vertical coupling embodiments, inaccordance with an embodiment of the invention.

FIG. 31 illustrates an exemplary HCSEL embodiment with mirror couplingof light out of the surface of the laser diode chip, in accordance withan embodiment of the invention.

FIG. 32 illustrates an exemplary HCSEL embodiment with grating couplingof light out of the surface of the laser diode chip, in accordance withan embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the invention may be found in a method and system fora light source assembly supporting direct coupling to an integratedcircuit. In various exemplary aspects of the invention, a light sourceassembly affixed to the chip may comprise a laser, a microlens, aturning mirror, an optical bench, and reciprocal and non-reciprocalpolarization rotating elements. The laser may generate an optical signalthat may be focused utilizing the microlens, which may comprise a balllens. The focused optical signal may be reflected at an angle defined bythe turning mirror. The reflected optical signal may be transmitted outof the light source assembly to one or more grating couplers in thephotonically enabled CMOS chip. The one or more grating couplers maycomprise polarization independent optical couplers. The laser maycomprise an edge-emitting semiconductor laser diode and/or a feedbackinsensitive laser diode. The light source assembly may comprise twoelectro-thermal interfaces between the optical bench, the laser, and alid affixed to the optical bench. The turning mirror may be integratedin a lid affixed to the optical bench by etching, or may be integratedin the optical bench.

FIG. 1A is a block diagram of an exemplary CMOS wafer comprisingoptoelectronic transceiver chips, in accordance with an embodiment ofthe invention. Each chip, or die, comprises Mach-Zehnder interferometer(MZI) modulators, surface light couplers for fiber coupling, germanium(Ge) photodetectors, low-loss waveguides and passive optics, a coupledlight source, and integrated electronics. By utilizing surface lightcoupling into and out of the chip, a standard CMOS process including ametal guard ring may be utilized. Similarly, by utilizing a singlecoupled light source with a photonically enabled CMOS chip, low cost,high performance optoelectronic transceivers are enabled.

Furthermore, the integration enables wafer-scale testing and screeningfor bad wafers and/or die, even during fabrication at the fab, using inline process monitors, and during subsequent wafer-scale testing.Conventional systems are tested after they are separated, the onlyexception being VCSELs. In an embodiment of the invention, the lasersource may be mounted to the CMOS integrated circuit for testing of theoptical and optoelectronic devices in the chip.

In an embodiment of the invention, simulation and verification of theentire OE signal path and low-speed control/power, and other blocks maybe completed before fabrication, using standard CMOS design tools, suchas standard tools that include simulation of optical devices in aSPICE-type simulator that are typically only used for electronics. Thisenables assurance of high-speed and optical signal integrity within thechip by design across all process/voltage/environmental corners, asopposed to the difficult task of ensuring signal integrity across PCBtraces and wires when connecting electronics-only laser drivers and TIAsto optical elements in conventional optics hybrid systems.

Similarly, it enables a reduction in bill of material (BOM) items withalmost no loss of yield due to element mismatch due to differenttechnologies (CMOS high-speed drivers with directly modulated III-Vlasers, TIAs with III-V photodetectors, for example) in the high-speedsignal path. The result is a significant reduction of assembly cost, anda higher yield.

Integrated CMOS optical and electrical functionality enables improvedreliability. For example, since there is no direct modulation of lasersor external modulators, but rather the modulation of a silicon junction,where the reliability is that of a CMOS chip. By utilizing a single edgeemitting CW laser instead of an array of discrete VCSELs, reliabilitymay be increased further, since edge emitting DFB and Fabry-Perot lasersexhibit increased reliability and are able to operate at highertemperatures. Furthermore, the system reliability is enhanced bystandard SOI CMOS process reliability, for example, and high volumecapability which enables lower cost optical data transmission.Similarly, the monolithic integration of electrical and opticalfunctionality eliminates reliability limitations of the interconnectionpackaging technologies inherent in non-monolithic systems.

Further functions integrated in the CMOS chip comprise: digitalcircuits, mixed signal A/D, D/A, voltage regulators, bypass/decoupling,and feedback loops to control chip over temperature, which removes theneed for temperature control via thermoelectric coolers, for example.This reduces power dissipation and cost. Further functionality comprisesa built-in self test to reduce external testing equipment requirementsand testing cost.

In addition, additional blocks from third parties may be integrated,such as SerDes and/or standard protocol blocks such as USB, PCI Express,for example.

In an embodiment of the invention, the CMOS optical and electricalintegration provides a port to next generation CMOS nodes to benefitfrom smaller linewidths and faster transistors, for example.

An optical source may be coupled to the CMOS chip to provide acontinuous-wave (CW) light beam that may be processed by the chip andtransmitted over optical fibers. The optical source comprises a III-V,or other semiconductor material, laser diode, for example, that may beaffixed to a support structure with one or more beam deflecting surfacesand/or devices that may enable coupling of the light into the CMOS chip.In an embodiment of the invention, the light is coupled into a gratingcoupler integrated in the chip which may result in optimum couplingefficiency when the light is transmitted to the surface with aparticular polarization and angle. Thus, the optical source may comprisepolarization control structures to optimize coupling efficiency into thechip.

In another or complimentary embodiment of the invention, an isolator isintegrated in the optical source to isolate the laser diode from signalsreceived from the grating coupler in the CMOS chip, which may adverselyaffect the operation of the laser diode.

FIG. 1B is a block diagram of a photonically enabled CMOS chip, inaccordance with an embodiment of the invention. Referring to FIG. 1B,there is shown optoelectronic devices on a CMOS chip 130 comprising highspeed optical modulators 105A-105D, high-speed photodiodes 111A-111D,monitor photodiodes 113A-113H, and optical devices comprising taps103A-103K, optical terminations 115A-115D, and grating couplers117A-117H. There is also shown electrical devices and circuitscomprising transimpedance and limiting amplifiers (TIA/LAs) 107A-107D,analog and digital control circuits 109, and control sections 112A-112D.Optical signals are communicated between optical and optoelectronicdevices via optical waveguides fabricated in the CMOS chip 130.

The high speed optical modulators 105A-105D comprise Mach-Zehnder orring modulators, for example, and enable the modulation of the CW laserinput signal. The high speed optical modulators 105A-105D are controlledby the control sections 112A-112D, and the outputs of the modulators areoptically coupled via waveguides to the grating couplers 117E-117H. Thetaps 103D-103K comprise four-port optical couplers, for example, and areutilized to sample the optical signals generated by the high speedoptical modulators 105A-105D, with the sampled signals being measured bythe monitor photodiodes 113A-113H. The unused branches of the taps103D-103K are terminated by optical terminations 115A-115D to avoid backreflections of unwanted signals.

The grating couplers 117A-117H comprise optical gratings that enablecoupling of light into and out of the CMOS chip 130. The gratingcouplers 117A-117D are utilized to couple light received from opticalfibers into the CMOS chip 130, and the grating couplers 117E-117H areutilized to couple light from the CMOS chip 130 into optical fibers. Theoptical fibers may be epoxied, for example, to the CMOS chip, and may bealigned at an angle from normal to the surface of the CMOS chip 130 tooptimize coupling efficiency.

The high-speed photodiodes 111A-111D convert optical signals receivedfrom the grating couplers 117A-117D into electrical signals that arecommunicated to the TIA/LAs 107A-107D for processing. In anotherembodiment of the invention, photodetectors may be used in thehigh-speed data path as monitor photodiodes to monitor the signalstrength, and as a feedback signal for control of the light sourceintensity, for example.

In an embodiment of the invention, optical terminations may be utilizedto eliminate unneeded or unused optical signals. The analog and digitalcontrol circuits 109 may control gain levels or other parameters in theoperation of the TIA/LAs 107A-107D. The TIA/LAs 107A-107D thencommunicate electrical signals off the CMOS chip 130.

The control sections 112A-112D comprise electronic circuitry that enablemodulation of the CW laser signal received from the splitters 103A-103C.The high speed optical modulators 105A-105D require high-speedelectrical signals to modulate the refractive index in respectivebranches of a Mach-Zehnder interferometer (MZI), for example. Thevoltage swing required for driving the MZI is a significant power drainin the CMOS chip 130. Thus, if the electrical signal for driving themodulator may be split into domains with each domain traversing a lowervoltage swing, power efficiency is increased.

The 4×10 Gb/s transceiver, with four channels of transmit and fourchannels of receive on a single chip may comprise high-speed analogelectronic circuits, high speed photodiodes 111A-111D, optical fibers,control circuits 112A-112D, high-speed optical modulators 105A-105D,modulator control circuits, taps 103A-103K, monitor photodiodes113A-113H, a CW laser, and optical waveguides. In the illustratedembodiment, with the exception of the CW laser and the optical fibers,which may be coupled to the surface of the chip, all of the componentsshown may be integrated in a chip fabricated using a standard CMOSprocess, and a guard ring may be used. Light is coupled in and out ofthe surface of the chip, permitting the use of a guard ring.

In an embodiment of the invention, all optical and electrical functionsof a high-speed optical data transceiver may be integrated in a singleCMOS SOI chip, except for the light generation, which may be coupledinto the chip via a laser source coupled to the surface of the chip. Inconventional telecom and datacom systems, these functions areaccomplished by separate components. For example, the laser andphotodetectors may be fabricated in III-V materials such as indiumgallium arsenide phosphide, for example. Furthermore, in conventionalsystems, the modulator/laser drivers and transimpedance amplifiers(TIAs) and receiver circuits may be fabricated in SiGe or CMOS chips. Inan embodiment of the invention, by integrating the electrical andoptical components on a single chip, multiple data channels may bereadily fabricated on a single die. This approach leads to a highlyscalable transmitter by replicating unit cells.

In an embodiment of the invention, the optical functionality that isintegrated on the chip comprises: waveguiding, optical coupling, lightsplitting, high and low speed optical modulation, light detection, andlight termination. Optical coupling comprises coupling light in and outof the chip via optical I/O, grating couplers, which may couple light infrom an external laser, and also couple light in and out of opticalfibers.

In an embodiment of the invention, splitting light may be enabled viasplitters and/or taps. Splitters and/or taps may split the laser lightfour or more ways so that a single laser can feed four or more channels,via 50% splitters, or to tap off a small portion of the light, 1 to 2%,for example, for monitoring the optical signal at the output of themodulators.

High-speed optical modulation, from 1 to 10 GB/s or higher, for example,may be utilized to convert electrical high-speed signals to opticalsignals. Low-speed optical modulation, indicated by the control sections112A-112D, may compensate for fabrication variations and environmentalchanges during operation, such as a change of temperature, for example.

Electrical control of optical functions integrated on the chip comprisesrouting light around the chip, similar to an electrical interconnect.High-speed analog circuits comprise: modulator drivers, transimpedanceamplifiers, limiting amplifiers, transmitters/receivers to drive traceson host PCB, and clock/data recovery (CDR). Low-speed analog circuitscomprise: monitor photodiode amplifiers, low-speed optical modulatordrivers, and laser drivers. In an embodiment of the invention, theelectrical functionality also comprises digital logic for interfacingwith a host and controlling chip, A/D and D/A converters. Furtherfunctionality comprises voltage converters, passives such as inductors,capacitors, and resistors, for example, and ESD protection circuits.

In an embodiment of the invention, the “CW Laser In” block 101 comprisesthe optical source described with respect to FIGS. 2A-33. The opticalcomponents in FIG. 1B integrated on the CMOS chip may utilize theoptical signal received from the CW Laser In 101 to generate modulatedoptical signals, via a Mach-Zehnder Interferometer modulator, forexample, that may be transmitted over the optical fibers. The modegenerated is suitable for transmission over single mode optical fiber.

FIG. 1C is a diagram illustrating an exemplary CMOS chip, in accordancewith an embodiment of the invention. Referring to FIG. 1C, there isshown the CMOS chip 130 comprising electronic devices/circuits 131,optical and optoelectronic devices 133, a light source interface 135,CMOS chip surface 137, an optical fiber interface 139, and CMOS guardring 141.

The light source interface 135 and the optical fiber interface 139comprise grating couplers that enable coupling of light signals via theCMOS chip surface 137, as opposed to the edges of the chip as withconventional edge-emitting devices. Coupling light signals via the CMOSchip surface 137 enables the use of the CMOS guard ring 141 whichprotects the chip mechanically and prevents the entry of contaminantsvia the chip edge. The light source interface 135 may comprise thelanding pads 135A with a thickness that may protect the CMOS chipsurface 137 from contact that could damage the surface when affixing thelight source to the CMOS chip 130. The landing pads 135A may beintegrated into the CMOS chip 130, such as through a metal deposition,or may comprise post-CMOS processing polymer deposition and patterning,for example.

The optical fiber interface 139 may enable the coupling of one or moreoptical fibers to the CMOS chip 130, and may comprise grating couplersfor near-vertical light coupling as compared to conventional systemswhich couple light through the chip edge, precluding the use of a guardring. The light source interface may enable the coupling of an externallight source to the CMOS chip, and may comprise a grating coupler, forexample. An optical source, such as a laser diode in a light sourcemodule, for example, may couple an optical signal into the light sourceinterface 135. The coupled light signal may be processed by the opticaland electronics devices in the CMOS chip 130.

The electronic devices/circuits 131 comprise circuitry such as theTIA/LAs 107A-107D and the analog and digital control circuits 109described with respect to FIG. 1A, for example. The optical andoptoelectronic devices 133 comprise devices such as the taps 103A-103K,optical terminations 115A-115D, grating couplers 117A-117H, high speedoptical modulators 105A-105D, high-speed photodiodes 111A-111D, andmonitor photodiodes 113A-113H.

FIG. 1D is a block diagram of an exemplary photonically enabled CMOSchip with guard ring, light source, and optical fiber cable, inaccordance with an embodiment of the invention. Referring to FIG. 1D,there is shown the CMOS chip 130 comprising the electronicdevices/circuits 131, the optical and optoelectronic devices 133, thelight source interface 135, pads 135A, the CMOS chip surface 137, andthe CMOS guard ring 141. There is also shown a fiber to chip coupler143, an optical fiber cable 145, and a light source assembly 147.

The CMOS chip 130 comprising the electronic devices/circuits 131, theoptical and optoelectronic devices 133, the light source interface 135,the CMOS chip surface 137, and the CMOS guard ring 141 may be asdescribed with respect to FIG. 1B.

In an embodiment of the invention, the optical fiber cable may beaffixed, via adhesive for example, to the CMOS chip surface 137. Thefiber to chip coupler 143 enables the physical coupling of the opticalfiber cable 145 to the CMOS chip 130.

The light source assembly 147 may be affixed, via optically transmissiveepoxy or solder, for example, to the CMOS chip surface 137, which maycomprise landing pads 135A to protect the CMOS chip 130 from physicaland electrical damage from excessive force or scratching, for example,during mounting of the assembly. In another embodiment of the invention,the light source assembly 147 may be soldered to contact pads on theCMOS chip 130 and then under filled or encapsulated to fill the spaceleft between the structures and protect the optical path. In this mannera high power light source may be integrated with optoelectronic andelectronic functionalities of one or more high-speed optoelectronictransceivers on a single CMOS chip.

The optical devices comprise MZI or ring modulators, waveguides,multiplexers, demultiplexers, splitters, taps, Y-junctions, directionalcouplers, and photodetectors, for example. The electronic devicescomprise, TIA's, voltage regulators, driver circuits, control circuits,A/D and D/A converters, limiting amplifiers, and laser drivers, forexample. The guard ring 141 may increase chip reliability by providing abarrier to contaminants diffusing into the edge of the chip and alsoreducing crack migration.

Light signals may be communicated from the light source assembly 147 tothe CMOS chip 130 via the light source interface 135 and to and from theoptical fibers in the optical fiber cable 145 via the optical fiberinterface 139 in the CMOS chip 130. In an exemplary embodiment of theinvention, the fiber to chip coupler 143 may be epoxied to the CMOS chip130, and the light source assembly 147 may be soldered, wire bonded,flip-chip bonded, and/or epoxied to the CMOS chip 130, for example.

In an exemplary embodiment of the invention, the light source assembly147 comprises an edge emitting compound semiconductor laser diodemounted on a support substrate. The compound semiconductor may comprisea plurality of layers of InP-based materials, such as GaInAsP, forexample, and the support substrate may comprise Si or a suitableceramic, for example. The support substrate may also comprise areflective surface for directing the laser optical mode down into agrating coupler on the CMOS chip 130. In an exemplary embodiment of theinvention, the reflective surface may be etched into the supportsubstrate.

In another embodiment of the invention, the light source assembly 147comprises an optical isolator comprising a faraday rotator and/or ahalf-wave plate and faraday rotator, depending on the polarizationrequirements as determined by the type, polarization, and physicalconfiguration of the light source utilized. For example, a laser diodein a TO-can may be utilized, which may be physically rotated in thelight source assembly eliminating the need for a half-wave rotator.Alternatively, in instances where an edge-emitting laser diode isutilized, rotation of the device may not be practical, thus a half-waveplate polarization rotator may be implemented.

The laser source in the light source assembly 147, may comprise acompound semiconductor laser diode, for example, and may emit light at awavelength suitable for communication over an optical fiber, such as 1.3or 1.55 microns, for example. The compound semiconductor laser mayoperate in continuous wave (CW) mode, with the modulation of the lightsignal performed by modulators integrated in the CMOS chip 130.

In another embodiment of the invention, the light source assembly 147comprises a compound semiconductor surface emitting laser, such as avertical cavity surface emitting laser (VCSEL) mounted on a supportsubstrate. The VCSEL may comprise compound semiconductor materials, suchas InP or GaAs-based materials, for example, and may emit light at awavelength suitable for communication over an optical fiber, such as 1.3or 1.55 microns, for example. The compound semiconductor laser mayoperate in continuous wave (CW) mode, with the modulation of the lightsignal performed by modulators integrated in the CMOS chip 130.

By integrating the optical functions within the CMOS chip 130, a singlelaser source may be utilized for a plurality of transmitting channels bysplitting the source into multiple signals via splitters, for example.In this manner, a high power laser may be utilized without requiringhigh speed operation of the laser.

FIG. 2A is a block diagram of an exemplary micropackaged light source,in accordance with an embodiment of the invention. Referring to FIG. 2A,there is shown a hermetically sealed light source assembly which enablesa small form factor with high coupling efficiency resulting in animproved link budget and more channels. A laser chip may generate lightthat may be focused via a micro-ball lens and pass through an isolatorbefore being reflected down by the turning mirror. This may enable lightto be directed down onto a CMOS chip into a grating coupler as shown inthe right schematic. The turning mirror may be formed into a surface ofthe support block under the laser chip and the ball lens, or may be adiscrete device placed on the support block. The micropackaged lightsource may be epoxied to the CMOS chip.

FIG. 2B is a light source assembly functional block diagram, a couplinggeometry diagram, and a micrograph of a functioning grating coupler, inaccordance with an embodiment of the invention. Referring to FIG. 2B,there is shown a functional block diagram of a light source assemblycomprising a laser source, a lens, an isolator, a beam-folding element,and a grating coupler interface. The isolator comprises a faradayrotator or a half-wave and faraday rotator, depending on thepolarization requirements as determined by the type, polarization, andphysical configuration of the light source utilized.

The coupling geometry block diagram illustrates the optical path fromthe laser source to the CMOS die via a lens, isolator, and foldingmirror. The light incident angle may range in angle from 1-60 degreesfrom normal, for example, to increase the coupling efficiency of lightcoupling into the grating coupler in the CMOS die.

The micrograph of a grating coupler demonstrates light being coupledinto the coupler on the left, and light coupling out of the coupler onthe right of the micrograph, demonstrating the two-way capability of thegrating coupler used to couple the light source assembly.

FIG. 2C is a block diagram of an exemplary photonically enabled CMOSchip, in accordance with an embodiment of the invention. Referring toFIG. 2C, there is shown a fabricated die illustrating an exemplarylayout comprising transmitter MZIs, receiver, Ge photodiodes andassociated electronics, configuration and control electronics, laseroptical input, and optical interfaces.

The Laser Optical Input comprises a grating coupler and may be utilizedto couple light into the CMOS chip from a light source assembly asdescribed with respect to FIG. 2E.

FIG. 2D is a block diagram of an exemplary optical input/output, inaccordance with an embodiment of the invention. Referring to FIG. 2D,there is shown a cross section and two scanning electron microscope(SEM) images of grating optical couplers. The grating couplers maycouple light vertically into and out of the chip, and may couple lightfrom various elements such as fibers, lasers, photodetectors, and planarlightwave chips. The grating couplers may utilize diffractive elementsto couple light.

In an embodiment of the invention, the coupler cross section mayillustrate the various layers of an exemplary grating coupler comprisinga silicon substrate, a buried oxide layer, grating layers, and adielectric stack. A waveguide may couple light into the coupler in theplane of the grating layer, for example. Loss coupling may be 1.5 dB orlower, for example, and may enable wafer-scale testing. In an embodimentof the invention, the grating coupler may enable 20× mode-sizeconversion laterally and longitudinally.

Vertical coupling of the light enables wafer-scale, known good dietesting before dicing, utilization of a CMOS chip guard ring, which isnot possible in conventional edge emitting configurations, and directattachment of the laser module and optical fibers on the chip.Wafer-scale testing enables full optoelectronic probing at full datarate, and possible built-in self test to improve yield and reduce costof testing. The self test comprises PRBS/error checker and opticalloopback, which is not possible without the integration of thephotonically enabled CMOS chip.

FIG. 3A is a schematic of a light source assembly comprising a laser, aball lens, an isolator, and a turning mirror incorporated in ahermetically sealed package, in accordance with an embodiment of theinvention. Each device comprises a discrete device and may be affixed toa support substrate comprising silicon or a ceramic material, forexample. Utilizing silicon substrates enables the utilization ofsemiconductor photolithography and etching techniques to define featuresfor affixing various devices such as the ball lens or laser diode, forexample.

The turning mirror may be a discrete device, or alternatively, may befabricated directly in the substrate, for example. Etched surfaces incrystalline surfaces may be utilized for reflective surfaces.

The light source assembly may be hermetically sealed via a lid affixedvia solder, epoxy, or glass frit, for example. Hermetic sealing of thelight source assembly may increase device lifetime by reducing oreliminating environmental effects on the optical elements in theassembly.

FIG. 3B is a block diagram of a support substrate with exemplarydimensions, in accordance with an embodiment of the invention. Thesquare hole near the center may be utilized to place a ball lens, andthe solder deposited around the outer edge of the substrate or matinglid part may be utilized as a solder line for hermetically sealing a lidas described with respect to FIG. 3A. The two square pads on the leftside of the top surface of the substrate may be utilized for bond padsenabling electrical connection to devices integrated on the substrate,for example.

FIG. 3C is a block diagram of a lid for hermetic sealing of the lightsource assembly, in accordance with an embodiment of the invention. Thelid may be etched to result in a cavity to allow for increased volumewithin the light source assembly. The lid may be affixed via epoxy,solder, or glass frit, for example, to the substrate to enable hermeticsealing.

FIG. 3D is a block diagram of a turning mirror, in accordance with anembodiment of the invention. Referring to FIG. 3D, there is shown aturning mirror with an angled reflective surface that may enabledirecting an optical signal down into a CMOS chip from an adjacent laserdiode. The angle of the reflective surface may be configured for optimumcoupling of the optical signal into a grating coupler in the CMOS chip.The turning mirror comprises an etched silicon block, or gold coatedglass, for example.

FIG. 3E is a block diagram illustrating an exemplary bond padconfiguration, in accordance with an embodiment of the invention.Referring to FIG. 3E, there is shown a light source assembly substratewith attached ball lens, laser diode, and electrical bond pads. The bondpads may enable electrical connection to the laser diode, for example.

FIG. 3F is a diagram of an exemplary light source assembly, inaccordance with an embodiment of the invention. Referring to FIG. 3F,there is shown an light source assembly 300 comprising an optical bench301, a precision mesa 303, a wire bond 305, a laser 307, arotator/isolator 311, alignment features 313, epoxy 315, a dielectricstack 317, contact pads 319, a lid 321, and a reflective surface 323.

The optical bench 301 may comprise a silicon optical bench, for example,and may comprise a micro-machined silicon substrate that may beconfigured to support optical, electrical, and/or optoelectronic devicesenabling accurate alignment of devices. Utilizing a micro-machinedsilicon substrate for the optical bench 301 enables the use ofanisotropic etch techniques to define features in the substrate, such asthe alignment features 313 or openings for the ball lens 309 or therotator/isolator 311.

The precision mesa 303 may comprise an insulating material with anaccurate thickness for placement on the optical bench 301, enablingaccurate alignment of the laser 307 with respect to other devices on theoptical bench 301, such as the ball lens 309.

The wire bond 305 may comprise a metal or other conductive material,gold for example, that may provide an electrical connection between thelaser 307 and the contact pads 319.

The laser 307 may comprise a semiconductor laser diode, for example, andmay be coupled epi-side down to the precision mesa 303. The laser 307may emit light at a wavelength that corresponds to the appropriatewavelength of light for the optical transceivers integrated in the CMOSchip 130 and the optical fiber cable 145 described with respect to FIGS.1B-1D.

The utilization of the precision mesa 303 and bonding the laser 307epi-side down enables accurate height control of the optical signal fromthe laser 307 with the ball lens 309. In addition, the laser 307 mountedepi-side down allows for better heat transfer to the large thermal massof the laser 307 substrate as well as into the precision mesa 303.

The ball lens 309 may comprise a microlens fabricated from an opticalmaterial formed in the shape of a sphere, for example, that may enablethe focusing of the optical signal generated by the laser 307 to adesired device, such as the rotator/isolator 311.

The rotator/isolator 311 may comprise reciprocal and/or non-reciprocalpolarization rotation capability that enables rotation of thepolarization vector of the optical beam generated by the laser 307. Thenon-reciprocal capability of the rotator/isolator 311 may comprise afaraday rotator. In addition, if a faraday rotator is utilized forisolation, the resulting optical mode may not be perpendicular to theplane of incidence at the CMOS chip 130, thus resulting in poor couplingefficiency. This may be corrected by adding a half-wave rotator, whichmay be integrated in the dielectric stack 317, for example. Thecombination of a faraday rotator and a half-wave plate results in thedesired polarization, TE polarized in the short dimension of the gratingcoupler, illustrated in FIGS. 2D and 22-26, at the surface of the CMOSchip 130 for optimum coupling efficiency.

The rotator/isolator 311 may be an optional component between the balllens 309 and the reflective surface 323, as the polarization rotationmay be enabled entirely by the dielectric stack 317 or the gratingcoupler in the CMOS chip 130 may be polarization independent, forexample. The rotator/isolator 311 may reduce and/or eliminate opticalfeedback to the laser 307 by rotating any reflected optical signalanother 45 degrees for a total of 90 degrees from the optical modeemitted by the laser 307 to reduce and/or eliminate feedback effects. Ininstances where a feedback insensitive laser is utilized for the laser307, the isolation function provided by a non-reciprocal polarizationrotator in the rotator/isolator 311 may not be required.

In addition to improved coupling efficiency, the rotator/isolator 311and a half-wave rotator integrated in the dielectric stack 317 mayprovide isolation from reflected optical signals to the laser 307. If noisolation is utilized, a feedback insensitive laser may be required,which may significantly increase cost.

The alignment features 313 comprise micro-machined features in theoptical bench 301 and may enable proper alignment of the light sourceassembly 300 to the CMOS chip 130.

The dielectric stack 317 may comprise pyrex or other glass layer, aquartz and/or half-wave plate, and a fabricated support substrate. Thehalf-wave plate may comprise single-crystal quartz, sapphire, or otherbirefringent material, and may enable the desired optical polarizationat the surface of the CMOS chip 130, which may be coupled below thedielectric stack 317.

The contact pads 319 may enable external electrical coupling to thelaser 307 via the wire bond 305. The lid 321 may be affixed via epoxy,solder, or glass frit, for example, to the optical bench 301 to enablehermetic sealing of the optical component space for improved lifetime.The reflective surface 323 may be fabricated into the lid 321, or maycomprise a separate optical component mounted to the optical bench 301,and may be operable to reflect the optical signal down towards the CMOSchip 130 mounted below the optical bench 301. In an embodiment of theinvention, the reflective surface 321 may be anisotropically etched inthe lid 321.

In operation, a bias voltage may be coupled to the laser 307 via thecontact pads 319 and the wire bond 305. An optical signal may begenerated by the laser 307 that may be focused onto the rotator/isolator311 via the ball lens 309. The rotator/isolator 311 may rotate thepolarization of the optical signal before the signal is reflecteddownward by the reflective surface 323. The polarization may be furtherrotated by a half-wave plate integrated in the dielectric stack 317 toconfigure the polarization to that of grating couplers integrated in theCMOS chip 130, such as the light source interface 135, described withrespect to FIG. 1C. The optical signal communicated to the CMOS chip 130may then be utilized to communicate signals over the optical cable fiber145 after processing by optoelectronic devices in the CMOS chip 130.

FIG. 3G is a diagram illustrating various views of the light sourceassembly, in accordance with an embodiment of the invention. Theplacement of the laser 307, the precision mesa 303, the ball lens 309,and the rotator/isolator 311 is shown in the various views. In thebottom right figure, the optical beam path is visible, including theangle from normal incidence at the CMOS chip interface at the bottom ofthe dielectric stack 317.

FIG. 3H illustrates an exemplary light source module, in accordance withan embodiment of the invention. Referring to FIG. 3H, there is shown alight source module 320 comprising the laser 307 mounted between theoptical bench 301 and the lid 321 together with the ball lens 309 andthe rotator/isolator 311 which may comprise an optical-isolator element.The laser 307 may comprise an edge emitting compound semiconductor laserdiode comprising a plurality of layers of InP-based materials, such asGaInAsP, for example. The optical bench 301 may comprise Si or asuitable ceramic, or various laminated materials (i.e. glass, quartz,etc.) for example.

The optical bench 301 may also comprise a reflective surface fordirecting the laser optical mode down into a grating coupler on the CMOSchip 130. In an exemplary embodiment of the invention, the reflectivesurface may be etched into the optical bench 301. In this embodiment thelid forms one-half of the package cavity whilst making electrical andthermal contacts to the laser 307. The laser 307 may be bonded to theoptical bench 301 and or lid 321 using a solder or other interfacematerial with desirable electrical and thermal properties. If the laser307 has it contacts on opposite sides of the chip then both thelid-to-laser interfaces (Electro-Thermal Interface A-325A) andbase-to-laser (Electro-Thermal Interface B-325B) may serve as electricaland thermal contacts to the laser 307. By placing both sides of thelaser 307 in intimate thermal contact with the large thermal masses suchas the lid 321 and the optical bench 301, the thermal resistance to thelaser 307 active area is reduced and the performance of the device isimproved by reducing the self-heating effect.

FIG. 3I illustrates an exemplary light source module with landing pads,in accordance with an embodiment of the invention. The landing pads 135Amay comprise metal or polymer pads, for example, that may provideprotection from physical, and subsequent electrical, damage to the CMOSchip 130 from the light source assembly 300 coupling process. Atransparent adhesive may be utilized to affix the light source assembly300 to the CMOS chip 130.

FIG. 3J illustrates an alternative embodiment of the light sourceassembly where the faraday rotator is encased within pyrex and quartz orsapphire layers below the silicon substrate. The laser diode may bemounted epi-side down on a precision mesa to enable accurate alignmentwith the ball lens. The various layers, such as the silicon substrate,the pyrex, and the quartz or sapphire layers, may be joined or bondedvia a low stress UV epoxy, such as Dymax OP29, for example.

FIG. 3K is a diagram illustrating various views of the light sourceassembly, in accordance with an embodiment of the invention. Theplacement of the laser diode, the precision mesa, the ball lens, and thefaraday rotator is shown in the various views. In the bottom rightfigure, the optical beam path is visible, including the angle fromnormal incidence at the CMOS chip interface at the bottom of the pyrexlayer via the embedded faraday rotator.

FIG. 4A is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.Referring to FIG. 4A, there is shown a silicon bench or substrate, anattached laser mount, a laser diode, a ball lens, a mirror element, alid, and pins for electrical connection.

The silicon bench may be polished on both sides and comprises an ARcoating to air on the cavity side and AR coating to glass or epoxy onthe side outside the cavity. The silicon bench comprises patternedinterconnections for the laser diode, and comprises pins for electricalconnection to electrical circuitry, such as on the CMOS chip to whichthe light source assembly is affixed.

The lid may enable hermetic sealing of the cavity and comprises siliconor metal, for example. The laser mount provides better or equal heatconduction than silicon to enable proper heat sinking for the laserdiode, which may be soldered or epoxied utilizing electro-thermaladhesive, such as silver epoxy, to the mount. The laser mount comprisesa pedestal etched in silicon, for example.

The ball lens comprises a high index optical material, such as glass,sapphire, or a gemstone material, for example, and may be 1 mm in radiusor less, for example. The placement of the ball lens may be defined bystructures etched into the silicon bench.

The mirror element comprises a reflective surface that may enablecoupling light nearly vertically out of the light source assembly asoriented in the figure. The optical signal may range in angle from 1-60degrees from normal, for example, to optimize coupling efficiency to agrating coupler in the CMOS chip. The optical mode comprises a beamwaist approximately 50 microns above the surface of the silicon bench tocoincide with grating coupler structures in the CMOS chip.

FIG. 4B is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.Referring to FIG. 4B, there is shown a silicon bench or substrate, anattached laser mount, a laser diode, a ball lens, a mirror element, acap and lid, and pins for electrical connection. The components aresubstantially similar to those described with respect to FIG. 4A, butwith an inverted orientation. Accordingly, the light emittinghorizontally from the laser diode and into the ball lens reflects offthe turning mirror and down through the transparent lid into a CMOSchip. The cap may comprise a walled cavity that enables hermetic sealingof the optical components to improve device lifetime. In this manner,the laser diode may be accessed from the top for thermal control—i.e.heatsinking away from the CMOS chip.

FIG. 4C is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.Referring to FIG. 4C, there is shown a silicon optical bench, anattached laser mount, a laser diode, a ball lens, an isolator or faradayrotator, a mirror element, a pyrex/quartz stack lid, and bond pads forelectrical connection. The lid comprises a pyrex/quartz stack which maybe orientated either way, with the pyrex or the quartz on top, andenables hermetic sealing of the optical components to improve devicelifetime. This embodiment with the electrical and optical interface onthe same side of the wafer allows wafer-scale fiber coupling testing ofthe laser package. The bottom side pad facilitates wire bonding afterattachment to the CMOS die. A membrane may be incorporated into thesilicon bench as shown in FIG. 4E or alternately one or more thermistorsmay be fabricated in the package as a hermeticity sensor.

FIG. 4D is a diagram illustrating an alternative embodiment of a lightsource assembly, in accordance with an embodiment of the invention.Referring to FIG. 4D, there is shown a silicon bench, an attached lasermount, a laser diode, a ball lens, an isolator or faraday rotator, amirror element, a pyrex/quartz stack lid, and bond pads for electricalconnection. The pyrex/quartz stack may be orientated either way, withthe pyrex or the quartz on top, and enables optical mode polarizationrotation.

FIG. 4E is a diagram illustrating an alternative embodiment of an lightsource assembly, in accordance with an embodiment of the invention.Referring to FIG. 4E, there is shown a silicon optical bench, anattached laser mount, a laser diode, a ball lens, an isolator or faradayrotator, a mirror element formed on a silicon ring, a pyrex/quartz stacklid, and bond pads for electrical connection. By utilizing bond pads onboth sides of the lid, electrical and optical testing of the lasersource may be enabled prior to affixing the assembly to the CMOS chip.In an embodiment of the invention, the topside electrical pad can beplaced in the dicing lanes on the wafer and diced away as part of thesingulation process leaving the bottom contact pad for wire bondingafter attach to the CMOS die. A membrane may be incorporated into thesilicon bench as shown or alternately one or more thermistors may befabricated in the package as a hermeticity sensor.

The lid comprises a pyrex/quartz stack which may be orientated eitherway, with the pyrex or the quartz on top, and enables hermetic sealingof the optical components to improve device lifetime. The silicon ringcomprises a silicon substrate that may be etched and coated to generateangled surfaces that may form mirror elements. A via may be etchedthrough the substrate to provide hermeticity testing via deflection of amembrane placed over the via.

FIG. 5 illustrates a TO-can implementation, in accordance with anembodiment of the invention. Referring to FIG. 5, there is shown animage of exemplary laser diode TO-cans and a cross-section of anexemplary TO-can with tilted optical window. The window may be tilted toenable the desired angle of incidence of the emitted light to thegrating coupler in the CMOS chip, for example.

The spacer enables the distance between the laser diode and the gratingcoupler in the CMOS chip to be defined such that the beam waist locationoptimizes coupling efficiency.

FIG. 6A illustrates a light source assembly with a TO-can and aedge-emitting laser diode implementation with an external heatsink, inaccordance with an embodiment of the invention. Referring to FIG. 6A,there is shown a silicon optical bench-type package and a TO-stylepackage illustrating two options for coupling light into a CMOS chip.Wire bonds may be utilized to provide electrical connectivity as shown.

FIG. 6B illustrates a light source assembly implementation having acavity-down wire bond edge-emitting laser diode with an externalheatsink, in accordance with an embodiment of the invention. Referringto FIG. 6B, there is shown a silicon optical bench-type package and acavity-down wire bond embodiment for coupling light into a CMOS chip.Wire bonds may be utilized to provide electrical connectivity as shown.

FIG. 7 illustrates an alternative embodiment with a cavity-up wire bondimplementation, in accordance with an embodiment of the invention.Referring to FIG. 7, there is shown a light source assembly affixed to aCMOS chip within a ceramic BGA package. The BGA package may bebump-bonded to a circuit board, for example. Wire bonds may be utilizedto provide electrical connectivity to the CMOS chip.

FIG. 8 illustrates a cavity-up wire bond implementation with heatspreader, in accordance with an embodiment of the invention. The CMOSchip may be affixed to a heat spreader to enable thermal control of theCMOS chip and may also enable wire bond electrical interconnects to theCMOS chip.

FIG. 9 is an external heatsink flip-chip implementation of a lightsource assembly, in accordance with an embodiment of the invention. TheCMOS chip which is bump-bonded to a carrier, which may also be bonded toa circuit board, for example. The CMOS chip may be coupled to anexternal heatsink for enhanced thermal conduction out of the chip.

FIG. 10 illustrates an exemplary module assembly comprising a TO-canoptical source implementation, in accordance with an embodiment of theinvention. Height limitations as per multi-source agreement (MSA)modules may determine the allowable wall thicknesses in the module aswell as placement of the TO can.

FIG. 11 illustrates exemplary flex circuit bend radius limitationswithin a module, in accordance with an embodiment of the invention. Tofit within an MSA module, the flex circuit comprises less than 1 mm bendradius.

FIG. 12 illustrates an alternative implementation comprising a laserdiode on a submount coupled to a leadless chip carrier (LCC) package, inaccordance with an embodiment of the invention. The laser diode may bemounted vertically on a submount to enable direct optical coupling to agrating coupler in the CMOS chip, but then may require accuratealignment control for optimal optical coupling efficiency.

A stamped lid with a molded aspheric lens may provide a hermetic sealfor the LCC package, as shown in the right diagram. The lid may beepoxied or soldered to the LCC package and may be integrated in a moduleas shown in FIG. 13.

FIG. 13 illustrates an LCC package module implementation, in accordancewith an embodiment of the invention. The module housing may besubstantially similar to the housing utilized for the flip-chipimplementation. The LCC package may be heatsinked to the module case,and a cavity may be utilized to provide clearance for the laser modulewithin the housing.

FIG. 14 illustrates the non-normal incidence of the optical mode fromthe LCC package, in accordance with an embodiment of the invention. Theangle provides for increased coupling efficiency with the gratingcoupler in the CMOS chip as normal incidence results in low ornegligible coupling efficiency in the grating coupler.

FIG. 15 illustrates an LCC package with a laser diode on submountimplementation, in accordance with an embodiment of the invention.Referring to FIG. 15, in the left figure, there is shown an LCC packagecomprising a laser diode on a submount or ceramic pedestal, a squareaspheric lens, and a prism. The outer edge of the top surface of the LCCpackage may be metalized for attachment of a window lid. The prism mayenable beam reflection for directing the optical signal out of the topof the LCC package and into a grating coupler on a CMOS chip. In theright figure, bond pads are implemented to provide electrical connectionto the laser diode.

The bottom figure in FIG. 15 illustrates a modified package with anintegrated isolator, in accordance with an embodiment of the invention.The isolator comprises a faraday rotator or a faraday and half-waverotator to provide appropriate polarization at the grating coupler inthe CMOS chip to which the LCC package is attached.

FIG. 16 illustrates a cavity-down implementation utilizing thermalgrease, in accordance with an embodiment of the invention. Referring toFIG. 16, there is shown a CMOS chip or die, a laser diode, a lens, anisolator, thermal grease, a prism, a window lid, and a wire bond. Thelaser diode may generate a CW optical beam that may be focused by thelens, then passed through the isolator, and then reflected by the mirrordown onto the CMOS die through the window lid. The wire bond may provideelectrical connectivity to the laser diode. The thermal grease mayprovide thermal conduction of heat out of the laser diode.

FIG. 17 is a simplified illustration of an exemplary light sourceassembly, in accordance with an embodiment of the invention. The laserdiode may be mounted on a mesa or pedestal and may emit light in thehorizontal direction into the ball lens, which may focus the light ontoa prism or angled reflective surface, which directs the light signaldown into the CMOS chip through the substrate. The substrate may betransparent or may comprise an optical window to allow the light to passthrough. In an embodiment of the invention, an isolator may beintegrated in the optical path for proper polarization at the CMOS chipsurface.

FIG. 18 illustrates an exemplary light source assembly enclosed in ahermetic package by a lid over the substrate, in accordance with anembodiment of the invention. The package comprises the laser diode, theball lens, and a prism, or reflective surface. In this manner, opticalcomponent lifetime may be increased by reducing or eliminatingenvironmental effects on the devices.

FIG. 19 illustrates an LCC package with a hermetically sealed windowlid, in accordance with an embodiment of the invention. The LCC packagemay be mounted on a CMOS chip to provide an optical signal into thesurface of the chip, while allowing thermal and electrical access to theback side of the package.

FIG. 20 illustrates the integration of the hermetically sealed LCCpackage onto the CMOS chip and associated printed circuit board andinterconnects, in accordance with an embodiment of the invention. Thecontact pads are accessible when the package is mounted to the CMOSchip, and the package may be aligned by maximizing the received opticalsignal in the CMOS chip before being epoxied in place.

FIG. 21 illustrates an alternative embodiment utilizing a ring todetermine vertical distance between the laser diode source assembly andthe CMOS die, in accordance with an embodiment of the invention. Thelaser diode generates an optical signal that may be focused by anaspheric lens, and then reflected by the prism up towards the CMOS die.The ring height may be configured to optimize coupling efficiency byplacing the beam waist at the appropriate point vertically in a gratingcoupler in the CMOS die.

FIG. 22 illustrates the desired polarization for increased gratingcoupling efficiency into a single polarization grating coupler in theCMOS chip, in accordance with an embodiment of the invention. Theincoming optical mode is TE polarized in the direction perpendicular tothe longest dimension of the coupler, as illustrated by E_(i). Inaddition, the optical mode may range in angle from 1-60 degrees fromnormal, for example, to the surface of the CMOS chip. In this manner, asilicon guided mode may be generated in the CMOS chip that may then beprocessed by optical devices in the chip.

FIG. 23. illustrates a TO can implementation polarization configuration,in accordance with an embodiment of the invention. To obtain maximizedgrating coupling efficiency by impinging an optical mode with theappropriate polarization, a TO can may be orientated with or without afaraday rotator, since a TO can may be easily rotated in place. If, inexample A, where there is no faraday rotator, the optical mode resultsin the correct polarization, by adding a faraday rotator, as in exampleB, the TO can may then be rotated to account for the rotation, resultingin the appropriate polarization.

The bottom right image demonstrates the ability to rotate the TO canwhen attached to the CMOS die.

FIG. 24 illustrates the challenge of supplying the appropriatepolarization when using a flat-stacked laser diode chip on a mesa, inaccordance with an embodiment of the invention. If a faraday rotator isutilized for isolation, the resulting optical mode is not perpendicularto the plane of incidence at the CMOS chip, thus resulting in poorcoupling efficiency. This is corrected by adding a half-wave rotator, asillustrated in FIG. 25.

FIG. 25 illustrates a laser diode source assembly with a faraday rotatorplus a half-wave plate, in accordance with an embodiment of theinvention. The combination of a faraday rotator and a half-wave plateresults in the desired polarization, TE polarized in the short dimensionof the grating coupler, at the surface of the CMOS chip for optimumcoupling efficiency. The desired polarization orientation for asingle-polarization grating coupler on the CMOS chip 130 may be achievedtogether with feedback isolation for the laser.

In addition to coupling efficiency, the faraday rotator and thehalf-wave rotator provide isolation from reflected optical signals tothe laser source. If no isolation is utilized, a feedback insensitivelaser may be required, which may significantly increase cost.

FIG. 26 illustrates the optical mode polarization without an isolator,in accordance with an embodiment of the invention. In this instance, theoptical mode may be at the appropriate polarization at the CMOS chipsurface, but optical modes may be reflected and/or transmitted back tothe optical source which may affect the output power of the laser diode,thus requiring a feedback insensitive laser. Cost factors may determinewhether an isolator or a feedback insensitive laser is preferred.

In instances where no laser isolation is utilized, a feedbackinsensitive laser may be required. The desired polarization orientationmay be achieved without polarization rotating elements.

In another embodiment of the invention, polarization-independentgratings and a feedback insensitive laser may be utilized, eliminatingthe need for rotators and isolators. Cost may be the determining factorin which embodiment to utilize, as polarization-independent gratings andfeedback insensitive lasers may be more costly and difficult tointegrate.

FIG. 27 illustrates several embodiments of external integration forcoupling light into a CMOS photonics chip, in accordance with anembodiment of the invention. Illustration 1) shows an embodiment withthe CMOS chip package and a laser diode in separate housings on aprinted circuit board. In this case the laser light source isfunctioning like an “optical power supply” in a manner similar to enelectrical power supply in a conventional electronic system.Illustration 2) shows an embodiment with the CMOS photonics chip and alaser diode integrated in a single housing mounted to a printed circuitboard. Illustration 3) shows an embodiment with the CMOS photonics chipand a laser diode in separate housings on a printed circuit board. Inthis embodiment, the “optical power supply” may use the same port as theoptical fibers coupled to the CMOS photonics chip.

FIG. 28 illustrates an exemplary co-packaging embodiment, in accordancewith an embodiment of the invention. A laser diode chip may be mountedon a planar lightwave circuit (PLC) with a reflective surface to directthe emitted light down into the CMOS photonics chip via a gratingcoupler. In an embodiment of the invention, a flex cable may be utilizedto couple the laser diode and PLC to a power source. In this manner,active alignment may be enabled.

FIG. 29 illustrates an exemplary co-packaging embodiment with a laserdiode mounted on a heat sink and angled holder, in accordance with anembodiment of the invention. The optical path may include anencapsulation material such as silicon or epoxy which can serve toprotect the optical path and improve reliability. A flex connector maybe utilized for electrical interconnection to the laser diode assembly.

FIG. 30 illustrates exemplary vertical coupling embodiments, inaccordance with an embodiment of the invention. The embodiment on theleft comprises a vertical cavity surface emitting laser (VCSEL)implementation demonstrating vertical coupling of light out of the laserdiode chip. In this manner, the laser diode may be directly mounted tothe CMOS photonics chip.

The embodiment in the middle illustrates an exemplary horizontal cavitysurface emitting laser (HCSEL) with an angled reflective surface thatcouples light from the laser cavity out of the surface of the laserdiode chip. In this manner, light may be coupled into the CMOS photonicschip with a suitable polarization and angle for the grating coupler.

The embodiment on the right illustrates a HCSEL with grating couplingout of the surface of the laser diode chip. The grating in the laserdiode enables surface emission of light. In this manner, the laser diodechip may be mounted to the CMOS photonics chip with light coupled intothe CMOS photonics chip with a suitable polarization and angle for thegrating coupler.

FIG. 31 illustrates an exemplary HCSEL embodiment with mirror couplingof light out of the surface of the laser diode chip, in accordance withan embodiment of the invention. By utilizing an angled mirror surface,light coupling back into the laser cavity may be reduced and/oreliminated. The mode polarization is shown in the lower left figure,illustrating the compatibility of the HCSEL structure with the gratingcoupler in the CMOS photonics chip.

FIG. 32 illustrates an exemplary HCSEL embodiment with grating couplingof light out of the surface of the laser diode chip, in accordance withan embodiment of the invention. By utilizing grating coupling, such asfrom a distributed Bragg reflector (DBR), an improved light spectrum,reduced linewidth, for example, from the laser diode may be enabled. TheHCSEL structure may enable definition of the polarization mode emittedby the laser diode, which enables suitable coupling to the gratingcoupler in the CMOS photonics chip.

In an embodiment of the invention, a method and system are disclosed fora light source assembly supporting direct coupling to an integratedcircuit. In this regard, a light source assembly affixed to aphotonically enabled CMOS chip 130 may comprise a laser 307, a microlens309, a turning mirror 323, an optical bench 301, and reciprocal andnon-reciprocal polarization rotating elements. The laser 307 maygenerate an optical signal that may be focused utilizing the microlens,which may comprise a ball lens 309. The focused optical signal may bereflected at an angle defined by the turning mirror 323. The reflectedoptical signal may be transmitted out of the light source assembly300/320 to one or more grating couplers 101/135 in the photonicallyenabled CMOS chip 130. The one or more grating couplers 101/135 maycomprise polarization independent optical couplers. The laser 307 maycomprise an edge-emitting semiconductor laser diode and/or a feedbackinsensitive laser diode. The light source assembly 300/320 may comprisetwo electro-thermal interfaces 325A and 325B between the optical bench301, the laser 307, and a lid 321 affixed to the optical bench 301. Theturning mirror 323 may be integrated in a lid 321 affixed to the opticalbench 301 by etching, or may be integrated in the optical bench 301.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A system for processing signals, the systemcomprising: a photonically enabled complementary metal-oxidesemiconductor (CMOS) chip comprising a laser, microlens, turning mirror,and an optical bench, said photonically enabled CMOS chip being operableto: generate an optical signal utilizing said laser; focus said opticalsignal utilizing said microlens; reflect said optical signal at an angledefined by said turning mirror; and transmit said reflected opticalsignal to one or more grating couplers in said photonically enabled CMOSchip.
 2. The system according to claim 1, wherein said photonicallyenabled CMOS chip further comprises a non-reciprocal polarizationrotator.
 3. The system according to claim 2, wherein said non-reciprocalpolarization rotator comprises a latching faraday rotator.
 4. The systemaccording to claim 1, wherein said photonically enabled CMOS chipfurther comprises a reciprocal polarization rotator.
 5. The systemaccording to claim 4, wherein said reciprocal polarization rotatorcomprises a half-wave plate.
 6. The system according to claim 5, whereinsaid half-wave plate comprises a dielectric stack comprising one or morebirefringent materials operably coupled to said optical bench.
 7. Thesystem according to claim 1, wherein said turning mirror is integratedin said optical bench.
 8. The system according to claim 7, wherein saidturning mirror reflects said optical signal to transmit through a lidoperably coupled to said optical bench.
 9. The system according to claim1, wherein said turning mirror is integrated in a lid operably coupledto said optical bench.
 10. The system according to claim 1, wherein saidphotonically enabled CMOS chip comprises two electro-thermal interfacesbetween said optical bench, said laser, and a lid operably coupled tosaid optical bench.
 11. The system according to claim 1, wherein saidmicrolens comprises a ball lens.
 12. The system according to claim 1,wherein said laser comprises a semiconductor laser diode.
 13. The systemaccording to claim 1, wherein said laser comprises an edge emittinglaser diode.
 14. The system according to claim 1, wherein said opticalbench functions as a mechanical support structure for one or moreoptical components of said photonically enabled CMOS chip and saidreflected optical signal passes through said optical bench.
 15. Thesystem according to claim 1, wherein said optical bench comprisessilicon.
 16. The system according to claim 1, wherein one or moreinterposers are integrated in said photonically enabled CMOS chip. 17.The system according to claim 16, wherein said one or more interposerscomprise metal pads integrated into said photonically enabled CMOS chip.18. The system according to claim 16, wherein said one or moreinterposers comprise one or more polymer pads deposited on saidphotonically enabled CMOS chip.
 19. A system for processing signals, thesystem comprising: a photonically enabled complementary metal-oxidesemiconductor (CMOS) chip comprising a laser, a microlens, a turningmirror, and an optical bench, said photonically enabled CMOS chip beingoperable to: generate an optical signal utilizing said laser; focus saidgenerated optical signal utilizing said microlens; reflect said opticalsignal at an angle defined by said turning mirror; and transmit saidreflected optical signal into said photonically enabled CMOS chip. 20.The system according to claim 19, wherein said photonically enabled CMOSchip further comprises a non-reciprocal polarization rotator.
 21. Thesystem according to claim 20, wherein said non-reciprocal polarizationrotator comprises a faraday rotator.
 22. The system according to claim20, wherein said non-reciprocal polarization rotator comprises alatching faraday rotator.
 23. The system according to claim 19, whereinsaid photonically enabled CMOS chip comprises two electro-thermalinterfaces between said optical bench, said laser, and a lid operablycoupled to said optical bench.
 24. The system according to claim 19,wherein said turning mirror is integrated in said optical bench.
 25. Thesystem according to claim 24, wherein said turning mirror reflects saidoptical signal to transmit through a lid operably coupled to saidoptical bench.
 26. The system according to claim 19, wherein saidturning mirror is integrated in a lid operably coupled to said opticalbench.
 27. The system according to claim 19, wherein said microlenscomprises a ball lens.
 28. The system according to claim 19, whereinsaid laser comprises a semiconductor laser diode.
 29. The systemaccording to claim 19, wherein said laser comprises an edge emittinglaser diode.
 30. The system according to claim 19, wherein said opticalbench functions as a mechanical support structure for one or moreoptical components of said photonically enabled CMOS chip and saidreflected optical signal passes through said optical bench.
 31. Thesystem according to claim 19, wherein said optical bench comprisessilicon.
 32. The system according to claim 19, wherein one or moreinterposers are integrated in said photonically enabled CMOS chip. 33.The system according to claim 32, wherein said one or more interposerscomprise metal pads integrated into said photonically enabled CMOS chip.34. The system according to claim 32, wherein said one or moreinterposers comprise one or more polymer pads deposited on saidphotonically enabled CMOS chip.
 35. A system for processing signals, thesystem comprising: a photonically enabled complementary metal-oxidesemiconductor (CMOS) chip comprising a laser, a microlens, a turningmirror, and an optical bench, said photonically enabled CMOS chip beingoperable to: generate an optical signal utilizing said laser; focus saidgenerated optical signal utilizing said microlens; reflect said opticalsignal at an angle defined by said turning mirror; and transmit saidreflected optical signal to one or more optical couplers in saidphotonically enabled CMOS chip.
 36. The system according to claim 35,wherein said laser comprises a semiconductor laser diode.
 37. The systemaccording to claim 35, wherein said laser comprises an edge-emittinglaser diode.
 38. The system according to claim 35, wherein saidphotonically enabled CMOS chip further comprises a reciprocalpolarization rotator.
 39. The system according to claim 38, wherein saidreciprocal polarization rotator comprises a half-wave plate.
 40. Thesystem according to claim 39, wherein said half-wave plate comprises adielectric stack comprising one or more birefringent materials operablycoupled to said optical bench.
 41. The system according to claim 35,wherein said photonically enabled CMOS chip comprises twoelectro-thermal interfaces between said optical bench, said laser, and alid operably coupled to said optical bench.
 42. The system according toclaim 35, wherein said turning mirror is integrated in a lid operablycoupled to said optical bench.
 43. The system according to claim 35,wherein said turning mirror is integrated in said optical bench.
 44. Themethod according to claim 43, wherein said turning mirror reflects saidoptical signal to transmit through a lid operably coupled to saidoptical bench.
 45. The system according to claim 35, wherein saidmicrolens comprises a ball lens.
 46. The system according to claim 35,wherein said one or more optical couplers comprise grating couplers. 47.The system according to claim 35, wherein said optical bench functionsas a mechanical support structure for one or more optical components ofsaid photonically enabled CMOS chip and said reflected optical signalpasses through said optical bench.
 48. The system according to claim 35,wherein said optical bench comprises silicon.
 49. The system accordingto claim 35, wherein one or more interposers are integrated in saidphotonically enabled CMOS chip.
 50. The system according to claim 49,wherein said one or more interposers comprise metal pads integrated intosaid photonically enabled CMOS chip.
 51. The system according to claim49, wherein said one or more interposers comprise one or more polymerpads deposited on said photonically enabled CMOS chip.
 52. A system forprocessing signals, the system comprising: a photonically enabledcomplementary metal-oxide semiconductor (CMOS) chip comprising a laser,a turning mirror, and an optical bench, said photonically enabled CMOSchip being operable to: generate an optical signal utilizing said laser;reflect said optical signal at an angle defined by said turning mirror;and transmit said reflected optical signal to one or more opticalcouplers in said photonically enabled CMOS chip.
 53. The systemaccording to claim 52, wherein said laser comprises a semiconductorlaser diode.
 54. The system according to claim 52, wherein said lasercomprises an edge-emitting laser diode.
 55. The system according toclaim 52, wherein said laser comprises a feedback insensitive laserdiode.
 56. The system according to claim 52, wherein said photonicallyenabled CMOS chip comprises two electro-thermal interfaces between saidoptical bench, said laser, and a lid operably coupled to said opticalbench.
 57. The system according to claim 52, wherein said turning mirroris integrated in a lid operably coupled to said optical bench.
 58. Thesystem according to claim 52, wherein said turning mirror is integratedin said optical bench.
 59. The system according to claim 58, whereinsaid turning mirror reflects said optical signal to transmit through alid operably coupled to said optical bench.
 60. The system according toclaim 52, wherein said photonically enabled CMOS chip further comprisesa microlens.
 61. The system according to claim 60, wherein saidmicrolens is operable to focus said generated optical signal.
 62. Thesystem according to claim 52, wherein said optical bench functions as amechanical support structure for one or more optical components of saidphotonically enabled CMOS chip and said reflected optical signal passesthrough said optical bench.
 63. The system according to claim 52,wherein said optical bench comprises silicon.
 64. The system accordingto claim 52, wherein one or more interposers are integrated in saidphotonically enabled CMOS chip.
 65. The system according to claim 64,wherein said one or more interposers comprise metal pads integrated intosaid photonically enabled CMOS chip.
 66. The system according to claim64, wherein said one or more interposers comprise one or more polymerpads deposited on said photonically enabled CMOS chip.